Résumé :
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Communication n° 544 Duchenne and the less frequent Becker muscular dystrophy (DMD/BMD) are X-linked recessive disorders caused by mutations in the gene encoding the dystrophin muscle skeletal protein. In contrast with the severe DMD form in which the protein is completely missing, BMD is a milder form in which dystrophin is present, but altered. Both forms invariably show high circulating muscle creatine kinase (CPK) levels. We report a 9 year old boy in whom a persistent CPK elevation was detected incidentally during routine blood screening at 3 years of age. The patient had no clinical symptoms of muscular dystrophy except mild calf hypertrophy. Muscle biopsy showed a mild necrotic myopathy. Molecular analysis identified a deletion of exon 48 of the dystrophin gene. Based on the molecular finding, the diagnosis of Becker muscular dystrophy was given, without prognosis of the age of onset and severity of the disease. When the patient was 9 years old and still asymptomatic, the parents asked for genetic counselling. Molecular analysis showed that the mother was heterozygous carrier, and that she surprisingly inherited the exon 48 deletion from her healthy 70 year old father. Only few cases of deletion of exon 48 have been reported and clinical manifestations are variable with few cases of DMD and BMD males, but also with asymptomatic carrier males of advanced age. Our observation shows that one must be careful when giving such presymptomatic molecular diagnoses in term of prognosis for the patient and for genetic counselling in carrier women.
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